Thanks so much for your help, everyone. I've been thinking about this a lot, and reading what other people have written in these forums.
One thing I learned about myself, or I guess about others, is that being able to be in love with more than one person at a time isn't really a typical trait for a monogamous person -but always has been for me. It helps me understand in a different light why it was always such a huge struggle for me to be faithful with boyfriends. Every time I fell in love with someone new I'd question the relationship I was in, because I didn't recognize the possibility that I could be truly in love with both. Lots of hurt and heartache came out of that. With marriage I haven't stopped to question whether my husband is right for me, because wouldn't have married him if I didn't believe that to my core. I guess that's why it has taken me by surprise to feel such a strength of love for another man. (I have gotten used to the crushes, but this love has shaken me up.)
I've checked in with my friend on this and sure enough, he has always had that capacity to love more than one as well, although his relationships have never been polyamorous -just spells of monogamy, sometimes broken by affairs, and spells of dating several women casually. Interestingly, his last wife left him for a friend of theirs, and when she told him, he offered the solution of the three of them living together. (She didn't go for it.) Anyway, this is one of the ways in which I feel like he understands me like others don't because we are similar.
As for talking to my husband about it, with or without a therapist... Recently we broached the subject of my being able to spend the night at the home of a man with whom I had no romantic interest whatsoever, in order to get a break from my kids when I hit a spell of depression. It was in fact my doctor, a friend of ours, who offered the guest room in his country home. My husband firmly opposed it. (This is a man who gives me everything I want, almost without exception, so when there are exceptions I know he feels strongly.) His opposition didn't come from jealousy or mistrust of my motives or even the doctor's, but solely from propriety -what it would look like to other people. He feared what people would think if they heard his wife was staying overnight at another man's home without him. He felt so strongly about this, he put it above my need for respite when I was depressed, above what the doctor thought would be good for me. In compromise, I spent a weekend at my dad's house. Longer drive, but happier husband.
This is not someone who would be able to accept his wife being in another man's bed, certainly. So I feel like a request is more likely to hurt him than to bring me any kind of peace. I know him well.
I think what I would like instead, is to put a damper on the sexual side of my feelings for my friend, and work towards being able to continue loving him in other ways. I can tell my husband he is important to me, and that sometimes I need to go talk to him, and I can tell him some of how that relationship feeds into my happiness and my marriage, and I will feel more truthful and less sneaky if I am not in it for the kisses. I am it in for the long term, and for the happiness of all of us. Really, my husband's happiness is more important than whatever I might feel in bed with my friend, and he and I have, as we have always said, the knowledge that we desire each other that much, and the ability to fantasize, and knowing that fantasies are not all too different from memories.
We all make sacrifices for those we love, and I can do this much. I think.